A long time ago, not so long ago, there was a demon king in this world. The demon lord possessed great power, with which he intended to destroy the world. Of course, the humans living in that world desperately resisted, The battle between humans and the demon king lasted a long, long time with many casualties. But one day, a hero appeared on the side of humanity, and the battle finally came to an end. After a fierce battle, the hero sacrificed himself to defeat the demon king.. Everyone thought that the world would not perish, that peace would come... --But when he fell down, the Demon King laughed, "I have a daughter. My daughter has as much power as me, no, more than that. When my daughter turns sixteen, this time the world will end." --and sixteen years later To protect the world, Emma must kill the demon king's daughter who emerges before she turns 16 and destroys the world. The hero's daughter heads to the tower where she was imprisoned. She only gets one chance, only when her birthday comes in three days. In order to wait for that, the hero's daughter had to spend three days in the tower with the Demon King's daughter, but--? [Translated from official website]